1. Field
This invention pertains to firearms, notably rifles. It is particularly directed to lever action firearms, and provides a lever linkage with better mechanical advantage than has been available in rack and pinion arrangements.
2. State of The Art
A number of firearm designs rely upon a bolt structure to urge cartridges into the chamber of the gun and to then lock into battery position to seal the chamber. The bolt typically includes a body portion and a bolt head portion configured to interact with stationary locking lugs. The bolt head is rotated either clockwise or counter clockwise selectively to lock the bolt into battery position or to unlock the bolt so that it may be moved away from the chamber. Rearward movement of the bolt (often called "breaking the bolt") causes rotation of the bolt head and usually activates other associated mechanisms of the firearm. These mechanisms may function to eject a spent cartridge, to retrieve a fresh cartridge from a magazine and to position the fresh cartridge for loading into the chamber by the bolt. Movement of the bolt rearward from its battery position also typically effects cocking of the firing mechanism of the firearm.
Firearm bolts have been operated by various means, including lever action linkages of different types. These linkages function to move the bolt to the rear, away from its battery position. Initial such movement rotates the bolt, thereby to disengage the bolt head from the locking lugs. Because of the large forces transmitted to these structures when the firearm is discharged, there is an inherent tendency for the bolt to bind at the lugs. Considerable rotational force is thus required to effect a disengagement.
A lever action includes a lever member pivotally connected to the frame of a firearm. An internal lever arm interacts with other components within the receiver portion of the firearm to, among other things, rotate and withdraw from battery position the bolt when the internal lever arm is actuated by movement of an oppositely extending external lever arm. For convenient and satisfying operation, it is desirable for the "stroke," that is, the travel required of the external lever arm to effect rotation and rearward travel of the bolt, to be "short," that is, involving a pivot motion of relatively few, typically less than about 100 degrees. Movement of the internal lever arm is inherently coordinated to movement of the external lever arm, thereby imposing a design constraint on the internal mechanical system driven by the lever member.
Rack and pinion systems are highly preferred for driving the bolts of commercially successful lever action firearms. The internal lever arm carries an integral rack element which drives a pinion gear, and the bolt caries an integral rack which is in turn driven by the pinion gear. The pinion gear may comprise a first stage or segment of relatively small diameter and a second stage of relatively large diameter. The first stage may be driven by the rack element carried by the internal lever arm. The second stage then drives the rack portion of the bolt. In this way, the travel of the bolt is amplified by the gear ratio of the two-stage pinion gear. This gear ratio inherently imposes a mechanical disadvantage on the system, however. That is, the pinion gear delivers a force of smaller magnitude to the bolt than that delivered to the pinion gear by the lever.
The rack and pinion system permits adequate bolt movement with a short lever stroke, but current arrangements provide insufficient rotational force to ensure reliable disengagement of the bolt head from the locking lugs, that is to "break the bolt," unless other steps are taken to relieve binding of the bolt head. The means generally employed is to relieve the contact surfaces between the bolt head and the locking lugs. A machined helical contact surface is typical of currently available rack and pinion lever action systems. Surface relief of this kind is detrimental to the accuracy achievable with a battery bolt firearm. Accordingly, lever action firearms are not generally as well regarded as bolt action firearms from the standpoint of accuracy. It is feasible to construct a conventional bolt action firearm with a flat contact surface between the locking lugs and the bolt head normal the axis of the bolt.
There remains a need for a rack and pinion system for a lever action firearm which will preserve the desirable features of current designs while providing sufficient rotational force to the bolt to avoid the necessity for relieving the contact surface between the locking lugs and the bolt head. Such a system would permit the construction of lever action firearms characterized by shooting accuracy approaching that of conventional bolt action designs.